1. Field of the Intention
The present invention relates to a piezoelectric device in which a piezoelectric film is formed over a substrate through an electrode by vapor phase deposition using plasma. The present invention also relates to a liquid discharge device using such a piezoelectric device.
2. Description of the Related Art
Currently, piezoelectric devices constituted by a piezoelectric film and electrodes are used, for example, as actuators installed in inkjet recording heads, and the like. In the piezoelectric devices, the piezoelectric film expands and contracts in correspondence with increase and decrease in the strength of an electric field which is applied from the electrodes to the piezoelectric film. In addition, size reduction and performance improvement in various electronic devices are currently demanded. For example, in the field of the inkjet recording heads, size reduction in piezoelectric devices is required so as to enable high-density mounting of the piezoelectric devices for improving image quality.
When the size of the piezoelectric devices is reduced, from the viewpoint of precision in machining and processing, it is considered preferable that the piezoelectric film in each piezoelectric device have the smallest possible thickness and exhibit satisfactory piezoelectric performance. However, when the thickness of the piezoelectric film obtained by the conventional sintering technique is reduced and approaches the size of the crystalline grains constituting the piezoelectric film, the influence of the dimensions and the shapes of the crystalline grains on the piezoelectric performance becomes unignorable. Therefore, the piezoelectric performance is likely to vary and deteriorate, and it is difficult to achieve sufficient performance. In order to avoid the influence of the crystalline grains as above, use of vapor phase deposition such as sputtering or PVD (physical vapor deposition), instead of the sintering technique, is currently under study as a thin-film formation technique for production of a thin piezoelectric film.
Nevertheless, even in the case where a thin piezoelectric film is produced by vapor phase deposition, the piezoelectric performance of the thin piezoelectric film tore greatly varies than the piezoelectric performance of the bulk sintered piezoelectric body, so that it is difficult to produce a piezoelectric film having sufficient piezoelectric performance. Therefore, some attempts to solve this problem, including an attempt to optimize the crystal structure, are currently being made.
Registered Japanese Patent No. 3705089 (hereinafter referred to as JP3705089) discloses a piezoelectric device having a lead-containing piezoelectric film constituted by crystalline grains, where the greater part of the crystalline grains have a columnar structure and composition which continuously or progressively varies along the thickness direction.
U.S. Pat. No. 7,145,285 (hereinafter referred to as U.S. Pat. No. 7,145,285) discloses a piezoelectric device having a two-layer laminated piezoelectric film and an orientation control layer which underlies the piezoelectric film and has satisfactory adhesiveness to a lower electrode.
Although JP3705089 reports that the piezoelectric device disclosed in JP3705089 has satisfactory piezoelectric characteristics and can be formed in small size, the film-formation process used in production of the piezoelectric device is complex. For example, precise control of applied voltage is performed for realizing the variations in the composition of the piezoelectric film along the thickness direction.
On the other hand, U.S. Pat. No. 7,145,285 reports that the piezoelectric device disclosed in U.S. Pat. No. 7,145,285 exhibits high piezoelectric performance and durability due to the provision of the orientation control layer. However, since the piezoelectric film has the two-layer structure, it is necessary to change the target composition and the film-formation condition, That is, the process for producing the piezoelectric device disclosed in U.S. Pat. No. 7,145,285 is complex.